Serial/Vin plate is located on the drivers side door post. You can see it between the hinges in this photo. This number will work in the decoders.
http://good-times.webshots.com/photo/2055765980102454676uUharUOverload springs were very common on these trucks both factory and after-market set-ups because they were work trucks.
Six-lug wheels are a good indication you are dealing with a 1/2-ton truck. Also in reference to your earlier post 1/2-ton models are usually more desireable then same year 3/4-tons. But it is also a personal preference thing, I love my 3/4-ton and I love 3-windows!
